Jimmy Fallon Was on Top of the World. Then Came Trump.

Once the undisputed juggernaut of the late-night category, Mr. Fallon’s “Tonight Show,” a celebrity-friendly cavalcade of games and gags, has seen its ratings decline in recent months. Meanwhile, his politically pointed competitor Stephen Colbert, who hosts CBS’s “The Late Show,” has closed what was once a formidable gap of nearly one million viewers.

The resurgent interest in left-leaning programming hasn’t helped Mr. Fallon, a former star of “Saturday Night Live” who has built his brand on his all-around entertainer’s skills and down-the-middle tastes. And as Mr. Fallon is well aware, viewers haven’t seen him in quite the same light since an interview he conducted with Mr. Trump in September, which was widely criticized for its fawning, forgiving tone. In a gesture that has come to haunt the host, he concluded the segment by playfully running his fingers through Mr. Trump’s hair.